“Open” surgery is known to be very demanding for patients. For this reason, practitioners are increasingly using minimally invasive operations in which medical instruments are inserted into a natural duct of the patient (vagina, rectum, auditory meatus, etc.) or into an artificial duct connected to the body of the patient (cannula, artificial vein, trocar, etc.).
In urology, it is known to perform a prostate biopsy in order to screen for possible prostate cancer. This involves taking tissue samples from within the prostate, said samples then being analyzed in a laboratory in order to detect the presence of any cancer cells. For this, the patient lies on his side. A medical instrument comprising an ultrasound sensor and a needle guide with a biopsy needle is then inserted into the natural duct formed by the rectum. Using the medical instrument, the surgeon perforates the colon wall in order to access the prostate and thus take tissue samples.
To perform the biopsy, the only images the surgeon can use are two-dimensional ones taken in real time by the ultrasound sensor. The surgeon therefore has to imagine a three-dimensional representation of the prostate in order to take the samples distributed regularly within the volume of the prostate. This therefore requires very great dexterity on the part of the surgeon.
Furthermore, the prostate is an extremely soft organ, such that simple contact by the needle, without the latter being driven into the prostate, is enough to deform said prostate. Thus, even if the surgeon thinks the samples have been taken correctly, it is possible that he has not pierced the prostate at exactly the required spot. There is then a risk that the samples have not been taken uniformly from the prostate.
Devices have recently appeared to help the surgeon perform the various types of aspiration very precisely.
New devices comprise probes that can provide three-dimensional images of the prostate. The operating principle of said planning is to plan theoretical positions for the aspirations and to study the deformation of the prostate during the biopsy. The theoretical aspiration plan is then modified depending on the study of deformation of the prostate so that the aspirations can be done at the right places. However, the correct positioning according to the new plan remains entirely dependent on the skill of the surgeon.
What is more, it is possible that the patient is not under local anesthesia and/or is not immobilized. This means that the patient, and thus all the tissues of the natural or artificial duct with which the medical instrument can come into contact, can move during the operation.
To assist the surgeon, devices for guiding a medical instrument are known comprising an articulated arm for moving a proximal end of the medical instrument. The surgeon can then control the articulated arm so that it blocks the medical instrument in a given position. However, guiding devices of this kind consider positions of the medical instrument that are defined in a reference system fixed with respect to the examination room in which the patient is placed.
However, the patient and/or his prostate can move, and this has two major implications.
Firstly, the prostate is not fixed with respect to the reference system in which the control of the position of the articulated arm is defined. It can therefore happen that the prostate has changed position between the moment when the desired position of the medical instrument is given to the articulated arm and the moment when this position is reached by the medical instrument. Thus, the target reached by the medical instrument may be correct from the point of view of the articulated arm in the fixed reference system but wrong from the point of view of the prostate: the puncture is not made in the intended area of the prostate.
Secondly, the point of entry of the medical instrument into the body of the patient moves with the patient. Thus, the articulated arm may oppose any movements of the patient, which can be uncomfortable for the patient and even damage some of the patient's tissues.
During the intervention, the point of entry of the medical instrument into the patient exposes the medical instrument to “parasite” forces which hide the tactile information useful to the surgeon, namely the stresses of interaction between the medical instrument and the targeted organ. For this reason, the surgeon is not fully aware of the stresses applied to the prostate and may cause considerable deformation and/or considerable movement of the prostate without even knowing.